PulseAudio

PulseAudio is a general purpose sound server intended to run as a middleware between your applications and your hardware devices, either using ALSA or OSS. It also offers easy network streaming across local devices using Avahi if enabled. While its main purpose is to ease audio configuration, its modular design allows more advanced users to configure the daemon precisely to best suit their needs.

Note: Some confusion may occur between ALSA and PulseAudio. ALSA includes a Linux kernel component with sound card drivers, as well as a userspace component, libalsa.[1] PulseAudio builds only on the kernel component, but offers compatibility with libalsa through pulseaudio-alsa.[2]

By default, PulseAudio is configured to automatically detect all sound cards and manage them. It takes control of all detected ALSA devices and redirects all audio streams to itself, making the PulseAudio daemon the central configuration point. The daemon should work mostly out of the box, only requiring a few minor tweaks.

While PulseAudio usually runs fine out of the box and requires only minimal configuration, advanced users can change almost every aspect of the daemon by either altering the default configuration file to disable modules or writing your own from scratch.

PulseAudio runs as a server daemon that can run either system-wide or on per-user basis using a client/server architecture. The daemon by itself does nothing without its modules except to provide an API and host dynamically loaded modules. The audio routing and processing tasks are all handled by various modules, including PulseAudio's native protocol itself (provided by module-native-protocol-unix). Clients reach the server through one of many protocol modules that will accept audio from external sources, route it through PulseAudio and eventually have it go out through a final other module. The output module does not have to be an actual sound output: it can dump the stream into a file, stream it to a broadcasting server such as Icecast, or even just discard it.

You can find a detailed list of all available modules at Pulseaudio Loadable Modules. To enable them you can just add a line load-module <module-name-from-list> to ~/.config/pulse/default.pa.

Configuration files

PulseAudio will first look for configuration files in the home directory ~/.config/pulse, and if they are not found, the system-wide configuration from /etc/pulse will be applied.

Tip:

It is strongly suggested not to edit system-wide configuration files, but rather edit user ones. Create the ~/.config/pulse directory, then copy the system configuration files into it and edit according to your need.

Make sure you keep user configuration in sync with changes to the packaged files in /etc/pulse/. Otherwise, PulseAudio may refuse to start due to configuration errors.

There is usually no need to add your user to the audio group, as PulseAudio uses udev and logind to give access dynamically to the currently "active" user. Exceptions would include running the machine headless so that there is no currently "active" user.

daemon.conf

This is the main configuration file to configure the daemon itself. It defines base settings like the default sample rates used by modules, resampling methods, realtime scheduling and various other settings related to the server process. These can not be changed at runtime without restarting the PulseAudio daemon. The defaults are sensible for most users, see the pulse-daemon.conf(5) manpage for additional information. Boolean options accepts any of these: true, yes, on and 1 as well as false, no, off and 0.

Note: PulseAudio does not perform tilde expansion on paths in this file. Use absolute paths for any files.

Expand to show notable daemon.conf options list

Option

Description

daemonize

Controls whether the server will daemonize itself and return. Set to no when debugging so you can see the debugging information on the terminal.

resample-method

Which resampler to use when audio with incompatible sample rates needs to be passed between modules (e.g. playback of 96kHz audio on hardware which only supports 48kHz). The available resamplers can be listed with $ pulseaudio --dump-resample-methods. Choose the best tradeoff between CPU usage and audio quality for the present use-case.

Tip: In some cases PulseAudio will generate a high CPU load. This can happen when multiple streams are resampled (individually). If this is a common use-case in a workflow, it should be considered to create an additional sink at a matching sample rate which can then be fed into the main sink, resampling only once.

avoid-resampling

With avoid-resampling = yes, PulseAudio automatically configures the hardware to the sample rate which the application uses, if the hardware supports this sample rate (needs PA 11 or higher)

Warning: Enabling this feature might cause audio distortion, therefore it is disabled by default, see the release notes for more information.

enable-remixing

When the input and output have a different channel count (for example, outputting a 6 channel movie into a stereo sink), pulse can either remix all the channels (default, yes) or just trivially map the channels by their name (left goes to left, right to right, all others ignored) when no

system-instance

If set to yes, run the daemon as a system-wide instance. Highly discouraged as it can introduce security issues. Useful on Multiseat systems, or headless systems that have no real local users. Defaults to no.

flat-volumes

flat-volumes scales the device-volume with the volume of the "loudest" application. For example, raising the VoIP call volume will raise the hardware volume and adjust the music-player volume so it stays where it was, without having to lower the volume of the music-player manually. Defaults to yes upstream, but to no within Arch.

Note: The default behavior upstream can sometimes be confusing and some applications, unaware of this feature, can set their volume to 100% at startup, potentially blowing your speakers or your ears. This is why Arch defaults to the classic (ALSA) behavior by setting this to no.

realtime-scheduling

If your kernel supports realtime scheduling (for instance, Realtime kernel or Linux-ck), set this to yes to ensure PulseAudio can deliver low-latency glitch-free playback. You can adjust realtime-priority as well to have it use the correct priority, especially when JACK is also running on the system.

nice-level

Since PulseAudio runs in userspace and involves inter-process communication, audio can be subject to dropouts if the daemon does not have enough CPU time to process the audio. The default usually is enough, but can be tweaked to give pulse the wanted priority over (or below) other applications.

exit-idle-time

If you want to run PulseAudio only when needed and use ALSA otherwise, you can set a delay in seconds after which the daemon will automatically shutdown after all clients are disconnected. Set it to -1 to disable this feature.

log-level

When debugging, you may want to increase the logging level of the daemon to see exactly why a specific module fails to load. High logging levels will sometimes print useful information such as detected minimum latency for the system, which can then be used to tweak default-fragments and default-fragment-size-msec.

default-sample-format

This usually does not need to be changed, but if your sound card's native format is different, performance and quality can be improved by setting the right format here.

default-sample-rate

The default sample rate user by pulse unless overriden at module level. Change this if your sound card does not support 44100Hz or if you wish to upsample all audio. See previous note about CPU usage.

alternate-sample-rate

To fix a common limitation where movies at 48000Hz were needlessly downsampled to 44100Hz, some modules support changing their sample rate dynamically to avoid resampling when possible. See manual for more in-depth information. This usually does not need to be changed.

default-channels

The default number of channels when not specified. Usually do not need any change as you can configure more channels on per-module basis.

default-fragments

Audio samples are split into multiple fragments of default-fragment-size-msec each. The larger the buffer is, the less likely audio will skip when the system is overloaded. On the downside this will increase the overall latency. Increase this value if you have issues.

default-fragment-size-msec

The size in milliseconds of each fragment. This is the amount of data that will be processed at once by the daemon.

default.pa

This file is a startup script and is used to configure modules. It is actually parsed and read after the daemon has finished initializing and additional commands can be sent at runtime using $ pactl or $ pacmd. The startup script can also be provided on the command line by starting PulseAudio in a terminal using $ pulseaudio -nC. This will make the daemon load the CLI module and will accept the configuration directly from the command line, and output resulting information or error messages on the same terminal. This can be useful when debugging the daemon or just to test various modules before setting them permanently on disk. The manual page is quite self-explanatory, consult pulse-cli-syntax(5) for the details of the syntax.

Tip:

Rather than being a complete copy, ~/.config/pulse/default.pa can start with the line .include /etc/pulse/default.pa and then just override the defaults.

Run $ pacmd list-sinks|egrep -i 'index:|name:' to list available sinks. The present default sink is marked with an asterisk.

Edit ~/.config/pulse/default.pa to insert/alter the set-default-sink command using the sink's name as the numbering cannot be guaranteed repeatable.

client.conf

This is the configuration file read by every PulseAudio client application. It is used to configure runtime options for individual clients. It can be used to set and configure the default sink and source statically as well as allowing (or disallowing) clients to automatically start the server if not currently running.

Configuration command

The main command to configure a server during runtime is $ pacmd. Run $ pacmd --help for a list options, or just run $ pacmd to enter the shell interactive mode and Ctrl+d to exit. All modifications will immediately be applied.

Once your new settings have been tested and meet your needs, edit the default.pa accordingly to make the change persistent. See PulseAudio/Examples for some basic settings.

Tip: leave the load-module module-default-device-restore line in the default.pa file untouched. It will allow you to restart the server in its default state, thus dismissing any wrong setting.

It is important to understand that the "sources" (processes, capture devices) and "sinks" (sound cards, servers, other processes) accessible and selectable through PulseAudio depend upon the current hardware "Profile" selected. These "Profiles" are those ALSA "pcms" listed by the command aplay -L, and more specifically by the command pacmd list-cards, which will include a line "index:", a list beginning "profiles:", and a line "active profile: <...>" in the output, among other things. "Profiles" correspond to different card input/output configurations, notably the number of available input/output channels.

The "active profile" can be set with the command pacmd set-card-profile INDEX PROFILE, with no comma separating INDEX and PROFILE, where INDEX is just the number on the line "index:" and a PROFILE name is everything shown from the beginning of any line under "profile:" to just before the colon and first space, as shown by the command pacmd list-cards. For instance, pacmd set-card-profile 0 output:analog-stereo+input:analog-stereo.

It may be easier to select a "Profile" with a graphical tool like pavucontrol, under the "Configuration" tab, or KDE System Settings, "Multimedia/Audio and Video Settings", under the "Audio Hardware Setup" tab. Each audio "Card", which are those devices listed by the command aplay -l, or again by the command pacmd list-cards, will have its own selectable "Profile". When a "Profile" has been selected, the then available "sources" and "sinks" can be seen by using the commands pacmd list-sources and pacmd list-sinks. Note that the "index" of the available sources and sinks will change each time a card profile is changed.

The selected "Profile" can be an issue for some applications, especially the Adobe Flash players, typically /usr/lib/mozilla/plugins/libflashplayer.so and /usr/lib/PepperFlash/libpepflashplayer.so. Often, these Flash players will only work when one of the Stereo profiles is selected, and otherwise, will play video with no sound, or will simply "crash". When all else fails, you might try selecting a different profile.

Of course, when configuring some variation of Surround Sound in PulseAudio, the appropriate Surround profile will have to be selected, before Surround Sound will work, or in order to do things like remap the speaker channels.

Running

PulseAudio on Arch has pulseaudio.socket enabled by default for the systemd/User instance. This means that PulseAudio will automatically start when needed.

Note:

To disable pulseaudio.socket, make sure that $XDG_CONFIG_HOME/systemd/user/ exists and run systemctl --user mask pulseaudio.socket.

Many desktop environments support XDG Autostart. In those desktop environments, PulseAudio will be launched automatically regardless of the socket activation status.

Back-end configuration

ALSA

If you have applications that do not support PulseAudio explicitly but rely on ALSA, these applications will try to access the sound card directly via ALSA and will therefore bypass PulseAudio. PulseAudio will thus not have access to the sound card any more. As a result, all applications relying on PulseAudio will not be working any more, leading to this issue. To prevent this, you will need to install the pulseaudio-alsa package. It contains the necessary /etc/asound.conf for configuring ALSA to use PulseAudio. Also make sure that ~/.asoundrc does not exist, as it would override the /etc/asound.conf file.

To prevent applications from using ALSA's OSS emulation and bypassing PulseAudio (thereby preventing other applications from playing sound), make sure the module snd_pcm_oss is not being loaded at boot. If it is currently loaded (lsmod | grep oss), disable it by executing:

ALSA/dmix without grabbing hardware device

Note: This section describes alternative configuration, which is generally not recommended.

You may want to use ALSA directly in most of your applications while still being able to use applications which require PulseAudio at the same time. The following steps allow you to make PulseAudio use dmix instead of grabbing ALSA hardware device.

Remove package pulseaudio-alsa, which provides compatibility layer between ALSA applications and PulseAudio. After this your ALSA apps will use ALSA directly without being hooked by Pulse.

GStreamer

OpenAL

OpenAL Soft should use PulseAudio by default, but can be explicitly configured to do so:

/etc/openal/alsoft.conf

drivers=pulse,alsa

By default, OpenAL does not allow pulseaudio to move audio streams to a different device. To change this, add the allow-moves option:

/etc/openal/alsoft.conf

[pulse]
allow-moves=true

libao

Edit the libao configuration file:

/etc/libao.conf

default_driver=pulse

Be sure to remove the dev=default option of the alsa driver or adjust it to specify a specific Pulse sink name or number.

Note: You could possibly also keep the libao standard of outputting to the alsa driver and its default device if you install pulseaudio-alsa since the ALSA default device then is PulseAudio.

Audio post-processing

PulseEffects

PulseEffects is a GTK advanced utility for applying audio effects to applications output or to microphone before sending its audio stream to a recording tool. The user has full control over which effects to apply and their order. To install it, choose between pulseeffects or pulseeffects-gitAUR.

You have to specify your card sink name, get it from pacmd list-sinks. In order to apply the changes, stop and restart Pulseaudio. The above configuration has empty control options using the default values.

To tweak the module with custom control parameters, fill them respecting the right order. Expand to show the options list.

Control option

Description

RMS/peak (0/1)

The blanace between the RMS and peak envelope followers. RMS is generally better for subtle, musical compression and peak is better for heavier, fast compression and percussion.

Attack time (ms)

The attack time in milliseconds.

Release time (ms)

The release time in milliseconds.

Threshold level (dB)

The point at which the compressor will start to kick in.

Ratio (1:n)

The gain reduction ratio used when the signal level exceeds the threshold. 1 means no compression; higher values stronger compression.

Knee radius (dB)

The distance from the threshold where the knee curve starts.

Makeup gain (dB)

Controls the gain of the makeup input signal in dB's.

Amplitude (dB)

The level of the input signal, in decibels.

Gain reduction (dB)

The degree of gain reduction applied to the input signal, in decibels.

QEMU

AlsaMixer.app

Here is a two examples where the first one is for ALSA and the other one is for pulseaudio. You can run multiple instances of it. Use the -w option to choose which of the control buttons to bind to the mouse wheel.

KDE Plasma Workspaces and Qt4

PulseAudio will automatically be used by KDE/Qt4 applications. It is supported by default in the KDE sound mixer. For more information see the KDE page in the PulseAudio wiki.

One useful tidbit from that page is that load-module module-device-manager should be loaded. This usually happens automatically at login through the script /usr/bin/start-pulseaudio-x11; if you find that the module is not loaded automatically you can consider adding it manually to /etc/pulse/default.pa. See #Switch on connect for possible conflicts with the module-switch-on-connect.

If the phonon-gstreamer backend is used for Phonon, GStreamer should also be configured as described in #GStreamer.

Audacious

Audacious natively supports PulseAudio. In order to use it, set Audacious Preferences -> Audio -> Current output plugin to 'PulseAudio Output Plugin'.

Music Player Daemon (MPD)

MPlayer

MPlayer natively supports PulseAudio output with the -ao pulse option. It can also be configured to default to PulseAudio output, in ~/.mplayer/config for per-user, or /etc/mplayer/mplayer.conf for system-wide:

/etc/mplayer/mplayer.conf

ao=pulse

mpv

mpv supports PulseAudio same as written for #MPlayer. Configuration in ~/.config/mpv/mpv.conf per-user, or /etc/mpv/mpv.conf system-wide.

guvcview

guvcview when using the PulseAudio input from a Webcam may have the audio input suspended resulting in no audio being recorded. You can check this by executing:

$ pactl list sources

If the audio source is "suspended" then modifying the following line in /etc/pulse/default.pa and changing:

load-module module-suspend-on-idle

to

#load-module module-suspend-on-idle

And then either restarting PulseAudio or your computer will only idle the input source instead of suspending it. guvcview will then correctly record audio from the device.

100 is a percentage. This requires the xorg-xset package. See Autostarting for a way to run these commands automatically when the X11 session is started.

Switch on connect

This is a module used to switch the output sound to the newly connected device. For example, if you plug in a USB headset, the output will be switched to that. If you unplug it, the output will be set back to the last device. This used to be quite buggy but got a lot of attention in PulseAudio 8.0 and should work quite well now.

If you just want to test the module then you can load it at runtime by calling:

$ pactl load-module module-switch-on-connect

If you want to make the change persistent you will have to add it to your local pulseaudio settings or to /etc/pulse/default.pa (system wide effect). In either case, add this line:

On KDE/Plasma5 you should furthermore disable module-device-manager. As soon as Plasma5 is started it loads (via start-pulseaudio-x11) the module module-device-manager for pulseaudio to manage the devices. But that module apparently conflicts with module-switch-on-connect. Therefore you should disable that module by editing /bin/start-pulseaudio-x11 and commenting the lines for KDE. Simply logout and login again and in order to renew your pulseaudio session. On connect switching should now work properly.

Script for switching analog outputs

Some sound cards present the option of multiple analog outputs, being switchable through using Pulseaudio profiles. But switching manually can become a chore, so you can use the following commands to switch it:

$ pactl set-sink-port 'number of the card' 'port'

This will set the default output to whatever port you chose.
Example:

$ pactl set-sink-port 0 "analog-output;output-speaker"

The values can be easily obtained using:

$ pactl list

Current output can be obtained through:

$ pactl list sinks | grep "active profile"| cut -d ' ' -f 3-

This process can be automated through a simple script. This script then can be given a shortcut by the user:

This script is intended to swap between two profiles. First checking the current profile then swapping it. Users are required to change the field 'active profile' according to the language pactl reports. Users might need to change the number of the card and the output to fit their machine.